The Hydrogeology of Crystal Spring with and Delineation of its Source Water Assessment Area

by
P. Allen Macfarlane
Kansas Geological Survey

KGS Open File Report 2003-35
October 2003

Executive Summary

Introduction

The Safe Drinking Water Act (SDWA 1996), as amended by Congress in 1996, established the Source Water Protection Program (SWPP). This program requires all states to submit individual public water supply Source Water Assessment Plans (SWAPs) to the US Environmental Protection Agency for approval and subsequent implementation by the state. The SWPP of the Kansas Department of Health and Environment (KDHE) closely follows the program structure laid out in the SDWA 1996 and is based on a three-way partnership among KDHE, the water supply, and technical assistance providers (KDHE, 1999). An integral part of the SWPP is the requirement for a delineation of each public water supply's source water assessment area (SWAA). The Kansas Geological Survey (KGS) conducts research on the water resources of Kansas and has the expertise to provide technical assistance to public water suppliers should it be needed in the process of SWAA delineation.

Crystal spring is the sole source of water for the city of Florence, located in the central part of the Flint Hills region of Kansas. The spring is fed by ground water that discharges from a limestone aquifer. Prior to this study there was little information available on which to define its catchment area. To fill this gap, the KGS proposed conducting a two-year study to delineate the spring catchment (source water assessment) area to the Kansas Source Water Protection Program of KDHE. The two goals for this project were to:

Complete a hydrogeologic study of the Crystal spring catchment and its surrounding area, and

Delineate the SWAA for Crystal spring based on the results of the hydrogeologic investigation.

The methods used to complete the hydrogeologic study of the project area included field mapping of the surface geology, inventory of springs and wells, water-level surveys, water sample collection and chemical analysis, surveys of the streambed in Martin and Bruno creeks, dye trace experiments, and automated high frequency water-level data collection in a monitoring well east of Martin Creek.

Catchment Hydrogeology and Water Quality

Alternating limestones and shales of the Permian age Chase Group crop out at the surface in the project area. The limestones are considered to be aquifers because they are more permeable than the shales and yield water to wells in the area. Within the project area, the primary aquifer zones are in the Barneston Limestone, which is approximately 80 ft (24.4 m) thick. The Barneston consists primarily of limestone, which is soluble in water moving downward from the surface. Acting over long periods of time, the continued movement of ground water through the limestones has created an integrated network of solution-widened fractures and conduits of varying size. The scale of these features ranges widely from fractures with apertures that are tenths of an inch (several millimeters) wide up to master conduits up to several feet (1 m) in diameter.

During this study, measured spring discharge ranged from slightly less than 28.3 L/s up to more than 510 L/s (1 ft3/s up to more than 18 ft3/s) and at least half of the time the discharge was 73.6 L/s (2.6 ft3/s). Spring discharge and turbidity are lower but dissolved solids concentrations are higher during dry than during wet periods.

Within its catchment ground water is transported through an integrated network of fractures and conduits to Crystal spring. Because of the variable size of the fractures and conduits, and the degree to which these features are connected to each other, rates of ground-water movement are highly variable. In the diffuse-flow part of the aquifer where the limestones are dominated by smaller-scale solution features, rates of ground water movement will be slower than in areas where larger scale conduits dominate (the conduit-flow part of the aquifer). Rapid entry and movement of ground water toward the spring is facilitated by sinkhole-like openings in the streambed of a reach of Martin Creek, approximately 2.5 mi to 3 mi (4 km to 4.8 km) north of the spring. Dye-trace experiments conducted during a relatively dry period indicated travel times through the ground water system of approximately 60 hours from sinkholes to the spring, indicating dye travel velocities of approximately 1 mi per day (1,500 m per day).

Analysis of the water-level data collected from wells shows that ground water moves in a southerly direction from the upland area toward Crystal spring and the Cottonwood River. As used here in this report, a catchment is defined as the area that provides recharge or is the source of water for a spring. In this case, the main source of water is infiltrated precipitation that falls on the upland surface north of the spring in the Martin Creek drainage. A well was installed 700 ft (213 m) east of Martin Creek to continuously monitor water levels in the Barneston Limestone. Water levels in the Barneston Limestone fluctuate over several 10s of feet (up to 10 m) depending on the occurrence and duration of wet and dry periods. Martin Creek was dry for much of the project period. Periods of high water levels in the aquifer coincide with streamflow events. Water levels are generally low during extended dry periods, such as occur during the summer, fall, and winter seasons and are high during the spring.

Spring discharge water quality reflects geochemical interactions between the ground water and a limestone aquifer. Calcium and bicarbonate dominate the dissolved ionic constituents. Dissolved solids concentrations ranged from 311 mg/L to 410 mg/L in samples of Crystal spring collected during the Winter and Spring 2002 water sampling events. To monitor changes in water quality, samples of water were collected from Crystal spring monthly from April 2002 to June 2003 and analyzed for sulfate, chloride, and nitrate concentrations. Sulfate, chloride, and nitrate ranged from 12 mg/L to 42.4 mg/L, 4.5 mg/L to 8.5 mg/L, and 2 mg/L to 9 mg/L, respectively.

The relationships between precipitation events and spring discharge, turbidity, and chemistry, precipitation and water levels in the aquifer near Martin Creek and the short travel time between the sinkholes and the spring indicate that the creek is a major contributor of water to Crystal spring during wet periods. The other major contributor is the drainage from the part of the aquifer where the solution openings are small scale and less well connected. This source sustains spring discharge during drier periods.

Source Water Assessment Area

Two SWAAs were delineated based on the results of this study: one associated with the reach of Martin Creek that traverses the Barneston Limestone outcrop belt, and the other associated with the Barneston aquifer outcrop where the spring is located. The factors considered in defining the SWAAs for Crystal spring include the following: soils, adsorption potential of the aquifer materials, direct vertical pathways to the ground-water system, overlying confining layers, and time-of-travel from sources of recharge to the spring.

SWAA 1 includes the Barneston outcrop belt near Martin Creek bounded on the southeast by the estimated limit of saturation in the aquifer. Most of the attention of this study has focused on the Martin Creek SWAA (SWAA 1). The results of the field investigation indicate that this area is an important source of recharge to Crystal spring.

The contribution of recharge to the Barneston aquifer outcrop area (SWAA 2) in the unnamed drainage and its consequent discharge at Crystal spring is unclear. Conservatively, it would seem reasonable to conclude that this part of the outcrop belt is a source area because of its proximity to the spring and the generally southward direction of ground-water flow in the Barneston. However, it is possible that the local ground-water flow system in this part of the drainage is entirely separate from the flow system that involves the Crystal spring and SWAA 1. Additional research needs to be carried out in this area to determine the level of significance of recharge from SWAA 2 to Crystal spring.